This proposal describes experiments that will seek to understand adhesion molecule function during nervous system development, and how specific connections are formed through the regulated action of cell adhesion molecules. The goal of the application is to understand how adhesion molecules regulate intracellular signaling events. The applicant will focus work on a recently described and poorly understood class of adhesion molecules, the receptor protein tyrosine phosphatases (RPTPs). The applicant has focused on PTPu, a unique RPTP that contains structural components similar to immunoglobulin superfamily proteins, cadherin adhesion molecules and PTPs. Previous studies by the applicant showed that the extracellular segment of PTPu mediates cell aggregation through homophilic binding of the immunoglobulin domain. Also, the intracellular domain of PTPu has catalytic activity and associates with cadherins. PTPu may signal in response to cell adhesion. This proposal will address the mechanism by which PTPu sends adhesive signals and the biological significance of this signal transduction. PTPu is abundant in many parts of the adult central nervous system and is developmentally regulated in the retina. The retina is one of the best characterized and experimentally tractable systems for studying both cell adhesion and development, particularly for neuronal migration and retinal layer formation (lamination) during development. Preliminary studies demonstrated that PTPu promotes neurite outgrowth of chick retinal ganglion cells. Three specific aims are proposed: (1) to determine whether PTPu phosphatase activity is required to induce neurite outgrowth on PTPu or N-cadherin substrates by: (a) determining the role of the PTPu phosphatase in the promotion of neurite outgrowth of chick retinal ganglion cell neurons, and (b) assessing the involvement of PTPu in regulation of the cytoskeleton using chick retinal ganglion cell neurons in border crossing assays; (2) to determine what signaling pathways are used by PTPu to transduce signals in response to adhesion by: (a) identifying downstream targets or substrates of PTPu; and (b) analyzing PTPu signal transduction pathway(s) in primary chick retinal cell cultures; and (3) to determine whether PTPu regulates retinal development by (a) investigating the role of PTPu in lamination of the chick retina during development; and (b) analyzing the role of PTPu in pathfinding of chick retinal ganglion cells during projection to the optic tectum.